This invention relates to an ion pump with a cathode of improved structure, particularly for pumping inert gases.
The ion pump or "ionization" pump according to the invention is of the "ion sputter" type, also know as "Penning pump", which is an efficient means for producing very high vacuums.
Various phenomena occur in the pumping element of the sputter ion pump which cooperate to lower the residual pressure. With regard to inert gases which are not subject to chemical reaction, the formation of the vacuum is due mainly to the phenomenon of sputtering of the cathode which is made of getter material which deposits on the anode or on the walls of the pumping element, entrapping and fixing thereon the gas molecules.
However, the efficiency of removal of inert gases and particularly of argon by the known sputter ion pumps is not satisfactory. Following up the phenomenological model outlined above it is in fact necessary for the ionized gas molecule to be neutralized on the cathode and to maintain a sufficient kinetic energy to permit it to be implanted on the walls of the pumping element to be buried thereon by the sputtered material.
With the structure of the conventional cathodes, even the most advanced ones, with bars arranged in grid fashion above and below an anode with cylindrical cells, the neutralizing impact of the ionizing inert gas with retention of kinetic energy sufficient for implantation in an extremely unlikely event. Consequently, the efficiency of pumping of inert gases and particularly argon does not exceed certain limits because of the situation outlined above.
It is an object of the present invention to provide a sputter ion pump which is capable of producing a very high vacuum due to the use of a cathode of improved structure whose geometry considerably increases the probability that the ionized inert gas will hit the surface of the cathode, thus forming fast molecules capable of being implanted on the walls of the pumping element.